On Tue, Feb 12, 2019 at 03:25:30PM +0100, Lorenzo Bianconi wrote: > > On Tue, Feb 12, 2019 at 03:09:53PM +0100, Lorenzo Bianconi wrote: > > > > > > > > (repost with corrected Lorenzo email) > > > > > > > > On Tue, Feb 12, 2019 at 02:45:50PM +0100, Stanislaw Gruszka wrote: > > > > > On Tue, Feb 12, 2019 at 02:24:47PM +0100, > > > > > [email protected] wrote: > > > > > > From: Lorenzo Bianconi <[email protected]> > > > > > > > > > > > > Use linear fragment and not a single usb scatter-gather buffer in > > > > > > mt76u > > > > > > {tx,rx} datapath if the usb controller has sg data length > > > > > > constraints. > > > > > > Moreover add disable_usb_sg module parameter in order to explicitly > > > > > > disable scatter-gather. SG I/O is not supported by all host drivers > > > > > > and > > > > > > some users have reported sg issues on AMD IOMMU. > > > > > > > > > > Again. This is not right approach. SG issues should be fixed > > > > > not workarounded. > > > > > > Hi Stanislaw, > > > > > > here we do not use SG, so num_sg is 0 and we use transfer_buffer. I do > > > not see how I am working around the issue. > > > > By avoiding SG buffer allocation and configuration which most likely > > need to be fixed. > > In my series I: > 1- set num_sg to 0 > 2- use transfer_buffer > > please correct me if I am wrong but in your solution you did the same since > AFAIK > PageHighMem is always 0 so you end up setting num_sg to 0 and using > transfer_buffer as well. Is my understanding correct?
Yes. But it still using all existing SG allocation and setup code and buffer is tracked in urb->sg[0]. > > > Moreover with this approach we avoid some unnecessary operation in the > > > hotpath > > > > What unnecessary operation ? > > the ones in mt76u_fill_bulk_urb() Your patches also add extra operations on hotpath due to urb->num_sgs and dev->usb.sg_en checks. Stanislaw
